SBS Technologies 466-1, Hardware Manual

Page: 84 / 110

Model 466-1 Adapter
74 Common Problems And Solutions
When an interface timeout occurs, the SBus adapter card terminates the
cycle on its side of the cable. The VMEbus adapter card, however,
continues to process the command. If this command is an access to the
VMEbus backplane, it continues with the VMEbus operation. If another
VMEbus access is attempted within 50
µ
sec the transaction may not
complete successfully, or a false BERR may be signaled that actually
originated on the previous cycle.
9.2.3 Local Status Register Bit 2: Interface Timeout
Any cable access to Dual Port RAM, a VMEbus device, or remote node CSR
lasting longer than the bus timeout interval, will cause an interface timeout.
An interface timeout is indicated by bit 2 of the Local Status Register being
set. The timeout does not clear until reset via the Local Command Register
reset mechanism.
Common causes of interface timeouts:
The same conditions that cause VMEbus errors (see section 9.2.2).
Multiple system clocks ( SYSCLK ) or no SYSCLK. There must be one
and only one SYSCLK in a VMEbus system.
Bus grant daisy chain jumpers are not configured properly, or the
Bus-
Grant/Bus-Request
jumpers on the VMEbus adapter card are not
configured properly.
If a VMEbus grant does not occur, it is usually due to a condition called
bus grant starvation. When many bus masters share the same bus grant
level, the requesting device closest to the arbiter in the bus grant daisy
chain receives the grant. Devices farther away from the arbiter are not
granted the bus as often. Bus grant delay is proportional to the number of
requesting devices on the same grant level.
Bus grant starvation usually is an intermittent condition, it may not occur
on every transfer
If bus grant starvation occurs, switch to a multi-level grant arbitration
scheme or move the VMEbus adapter card closer to the bus arbiter in slot
1.